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White-Bellied Sea Eagle
The white-bellied sea eagle (Haliaeetus leucogaster), also known as the white-breasted sea eagle, is a large diurnal bird of prey in the family Accipitridae. Originally described by Johann Friedrich Gmelin in 1788, it is closely related to Sanford's sea eagle of the Solomon Islands, and the two are considered a superspecies. A distinctive bird, the adult white-bellied sea eagle has a white head, breast, under-wing coverts and tail. The upper parts are grey and the black under-wing flight feathers contrast with the white coverts. The tail is short and wedge-shaped as in all Haliaeetus species. Like many raptors, the female is slightly larger than the male, and can measure up to 90 cm (35 in) long with a wingspan of up to 2.2 m (7.2 ft), and weigh 4.5 kg (9.9 lb). Immature birds have brown plumage, which is gradually replaced by white until the age of five or six years. The call is a loud goose-like honking. Resident from India and Sri Lanka through Southeast Asia to Australia on coasts and major waterways, the white-bellied sea eagle breeds and hunts near water, and fish form around half of its diet. Opportunistic, it consumes carrion and a wide variety of animals. Although rated as Least Concern globally, it has declined in parts of southeast Asia such as Thailand, and southeastern Australia. It is ranked as Threatened in Victoria and Vulnerable in South Australia and Tasmania. Human disturbance to its habitat is the main threat, both from direct human activity near nests which impacts on breeding success, and from removal of suitable trees for nesting. The white-bellied sea eagle is revered by indigenous people in many parts of Australia, and is the subject of various folk tales throughout its range. Description The White-bellied Sea-Eagle is a large raptor that has long, broad wings and a short, wedge-shaped tail. It measures 75–85 cm in length, and has a wingspan of 180–220 cm. Females weigh between 2.8 and 4.2 kg, and are larger than the males, which weigh between 2.5 and 3.7 kg (Clunie 1994; Marchant & Higgins 1993). The plumage of adult birds is predominantly white and grey. The head, breast and belly, and the feathering on the legs, are white. The back and upper surfaces of the wings are grey, although the wings have black tips. The undersides of the wings are greyish-black around the distal edges, with a smaller area of white along the leading edge. The tail is grey at the base, and has a white tip. The bill is bluish-grey with a blackish tip, the iris is dark brown, and the legs and feet are a cream colour (Clunie 1994; Marchant & Higgins 1993). The juveniles differ from the adults in appearance in having predominantly dark brown plumage on the upper parts, except for the creamy colouring on the head, and creamy markings over the rest of the upper parts. The underside of the body is a similar colour to the upper parts, but becomes paler with wear. The under side of the wing is patterned with a mixture of orange-buff, white, dark brown and dark grey. There is a gradual transition from the brown and cream plumage of juvenile birds to the white and grey plumage of the adults. This transition is completed across a series of moults, over a period of several years (Clunie 1994; Marchant & Higgins 1993). The White-bellied Sea-Eagle is generally seen singly or in pairs, though it may occasionally congregate around sites where food is abundant (Marchant & Higgins 1993). Habitat The White-bellied Sea-Eagle is found in coastal habitats (especially those close to the sea-shore) and around terrestrial wetlands in tropical and temperate regions of mainland Australia and its offshore islands. The habitats occupied by the sea-eagle are characterised by the presence of large areas of open water (larger rivers, swamps, lakes, the sea). Birds have been recorded in (or flying over) a variety of terrestrial habitats (Marchant & Higgins 1993). The species is mostly recorded in coastal lowlands, but can occupy habitats up to 1400 m above sea level on the Northern Tablelands of NSW and up to 800 m above sea level in Tasmania and South Australia (Marchant & Higgins 1993). Birds have been recorded at or in the vicinity of freshwater swamps, lakes, reservoirs, billabongs, saltmarsh and sewage ponds (Boekel 1976; Favaloro 1944; Gosper 1981; Marchant & Higgins 1993). They also occur at sites near the sea or sea-shore, such as around bays and inlets, beaches, reefs, lagoons, estuaries and mangroves (Abbott 1982; Boekel 1976; Favaloro 1944; Gosper 1981; Smith 1985). Terrestrial habitats include coastal dunes, tidal flats, grassland, heathland, woodland, forest (including rainforest) and even urban areas (Bell 1984a; Czechura 1984a; Harris 1980; Johnson & Hooper 1973; Longmore 1978; Quinn 1969; Roberts & Ingram 1976; Smith 1984). Breeding has been recorded on the coast, at inland sites, and on offshore islands (Marchant & Higgins 1993). Breeding territories are located close to water, and mainly in tall open forest or woodland (Emison & Bilney 1982; Marchant & Higgins 1993), although nests are sometimes located in other habitats such as dense forest (including rainforest) (Rhodes 1959), closed scrub or in remnant trees on cleared land (Emison & Bilney 1982). The White-bellied Sea-Eagle generally forages over large expanses of open water; this is particularly true of birds that occur in coastal environments close to the sea-shore, where they forage over in-shore waters (Marchant & Higgins 1993; Smith 1985). However, the White-bellied Sea-Eagle will also forage over open terrestrial habitats (such as grasslands) (Marchant & Higgins 1993; Sedgwick 1978). Birds may move to and congregate in favourable sites during drought or food shortage (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993; Shephard et al. 2005a). There are no published sources that state that the White-bellied Sea-Eagle occurs in any threatened ecological communities. However, given the widespread distribution of the species, its ability to make long-distance movements, and the broad range of habitats that it may be recorded in or flying over, it is possible that the sea-eagle may occur in one or more of the threatened communities listed under the EPBC Act 1999. The White-bellied Sea-Eagle is not known to associate with any other listed threatened species. Life Cycle The White-bellied Sea-Eagle first breeds at approximately six years old (Fleay 1948; Marchant & Higgins 1993). The mortality rate is high amongst newly-independent young birds, but if juveniles survive to breeding age they may live for up to 30 years (PWS Tas 2006). The White-bellied Sea-Eagle breeds in solitary and monogamous pairs that mate for life. However, if one member of the pair dies, it is quickly replaced (Clunie 1994; Favaloro 1944; Marchant & Higgins 1993). The breeding season extends from June to January (or sometimes February) in southern Australia, but begins one or two months earlier in northern Australia, for example, eggs are laid from June to September (or sometimes later) in southern Australia, and from May to August in northern Australia (Bilney & Emison 1983; Favaloro 1944; Marchant & Higgins 1993). The nest is a large structure composed of sticks and lined with leaves, grass or seaweed (Favaloro 1944; Marchant & Higgins 1993). Nests may be built in a variety of sites including tall trees (especially Eucalyptus species), bushes, mangroves, cliffs, rocky outcrops, caves, crevices, on the ground or even on artificial structures (Abbott 1982; Bilney & Emison 1983; Cupper & Cupper 1981; Emison & Bilney 1982; Favaloro 1944; Marchant & Higgins 1993; Whitlock 1919). Pairs usually return to the same breeding territory each year, and often the same nest, although territories tend to contain one or two additional, less developed nests (Favaloro 1944; Marchant & Higgins 1993). Breeding pairs tend to be widely dispersed, and are generally separated by distances of several kilometres or more (Bilney & Emison 1983; Clunie 1994; Fleay 1948; Garnett & Bredl 1985; Marchant & Higgins 1993), though on offshore islands pairs may be located quite close together. On Barrow Island, Western Australia, seven occupied nests were located within a radius of 9.5 km (Whitlock 1919). The eggs of the White-bellied Sea-Eagle are white or dull white in colour (Cupper & Cupper 1981; Marchant & Higgins 1993). Clutches usually consist of two eggs, but can be between one and three eggs (Marchant & Higgins 1993). The eggs are incubated for approximately six weeks (Bilney & Emison 1983). Most incubation is done by the female (P. Olsen 2005a, pers. comm.). The nestlings, which are fed by both parents, remain in the nest for 65–70 days or more (Brown & Amadon 1968; Cupper & Cupper 1981). The fledged young are fed by the adults for up to three months after leaving the nest. They are then driven out of the breeding territory by their parents approximately four months after fledging (Hollands 2003). Little information is available on breeding success. In the Gippsland Lakes region, Victoria, from 1978 to 1981, of 37 active sea-eagle nests observed, eight (22%) fledged no young, 19 (51%) fledged one young and ten (27%) fledged two young. Productivity was greater in native vegetation (forest, woodland, scrub) than it was in pastures with scattered tall trees, for example, sea-eagles fledged 1.2 young per occupied territory in tall open forest and 0.2 young per occupied territory in pasture (Bilney & Emison 1983). At Kapalga, in the Northern Territory, in 1981, only two of 13 pairs were successful in producing young (Marchant & Higgins 1993). In clutches where two eggs are laid, usually only one young is fledged (Cupper & Cupper 1981; Marchant & Higgins 1993). Pairs will lay a second clutch if the first is unsuccessful (Favaloro 1944). Behavior The white-bellied sea eagle is generally territorial; some birds form permanent pairs that inhabit territories throughout the year, while others are nomadic. The species is monogamous, with pairs remaining together until one bird dies, after which the surviving bird quickly seeks a new mate. This can lead to some nest sites being continuously occupied for many years (one site in Mallacoota was occupied for over fifty years). Immature birds are generally dispersive, with many moving over 50 km (31 mi) away from the area they were raised. One juvenile raised in Cowell, South Australia was reported 3,000 km (1,900 mi) away at Fraser Island in Queensland. A study of the species in Jervis Bay showed increases in the numbers of immature and subadult birds in autumn, although it was unclear whether these were locally fledged or (as was considered more likely) an influx of young birds born and raised elsewhere in Australia. Birds are often seen perched high in a tree, or soaring over waterways and adjacent land. They are most commonly encountered singly or in pairs. Small groups of white-bellied sea eagles sometimes gather if there is a plentiful source of food such as a carcass or fish offal on a ship. Much of the white-bellied sea eagle's behaviour, particularly breeding, remains poorly known. Breeding The breeding season varies according to location—it has been recorded in the dry season in the Trans-Fly region and Central Province of Papua New Guinea, and from June to August in Australia. A pair of white-bellied sea eagles performs skilful displays of flying before copulation: diving, gliding and chasing each other while calling loudly. They may mirror each other, flying 2–3 m (6.6–9.8 ft) apart and copying each other swooping and swerving. A talon-grappling display has been recorded where the pair will fly high before one flips upside down and tries to grapple the other's talons with its own. If successful, the two then plunge cartwheeling before separating as they approach the ground. This behavior has also been recorded as an aggressive display against a Wedge-Tailed Eagle The white-bellied sea eagle usually chooses tall trees or man-made pylons to nest in. Often, locations are sought where there is a tall dead tree or high branch with good visibility which can be used as a perch to survey the surrounding area, which is generally a low-lying locale near water with some forest cover. The perch becomes covered in faeces and pellets and animal remains litter the immediate surrounding area. The nest is a large deep bowl constructed of sticks and branches, and lined with such materials as grass or seaweed. Yearly renovations result in nests getting gradually bigger. Nests are generally sited in the forks of large trees overlooking bodies of water. Old nests of wedge-tailed eagles or whistling kites have been renovated and used. Cliffs are also suitable nesting sites, and on islands nests are sometimes built directly on the ground. A breeding pair, with the male being more active, spends three to six weeks building or renovating the nest before laying eggs. Normally a clutch of two dull, white, oval eggs are laid. Measuring 73×55 mm, they are incubated over six weeks before hatching. The young are semi-altricial, and covered in white down when they emerge from the egg. Initially, the male brings food and the female feeds the chicks, but both parents feed the chicks as they grow larger. Although two eggs are laid, it is unusual for two young to be reared successfully to fledging (leaving the nest). One egg may be infertile, or the second chick may die in the nest. If the first clutch is lost, the parents may attempt a second brood. Nestlings have been recorded fledging when 70 to 80 days old, and remaining around the parents' territory for up to six months or until the following breeding season. Feeding The White-bellied Sea-Eagle feeds opportunistically on a variety of fish, birds, reptiles, mammals and crustaceans, and on carrion and offal (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993; Rose 2001a). The White-bellied Sea-Eagle hunts its prey from a perch, or whilst in flight (by circling slowly, or by sailing along 10–20 m above the shore). When a prey item is located, the sea-eagle usually launches into a dive or shallow glide to snatch its prey, usually in one foot, from the ground or water surface (Clunie 1994; del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993). Prey is usually carried to a feeding platform or (if small) consumed in flight, but some items are eaten on the ground (Ferguson-Lees & Christie 2001; Marchant & Higgins 1993). In addition to these behaviours, the White-bellied Sea-Eagle will sometimes steal prey from seabirds and other raptors, and it has also been recorded following harvesters and dolphins to feed on flushed prey (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993). Movement Patterns The White-bellied Sea-Eagle is described as a breeding resident throughout much of its range in Australia (Marchant & Higgins 1993). Breeding adult birds are generally sedentary (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993), although they forage over large areas (Ferguson-Lees & Christie 2001) and are capable of undertaking long-distance movements (Marchant & Higgins 1993). They can also move in response to drought or a shortage of food (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993; Shephard et al. 2005a). Conversely, immature birds, and also some adult birds, undertake dispersal (del Hoyo et al. 1994; Ferguson-Lees & Christie 2001; Marchant & Higgins 1993). Immature birds are capable of travelling extremely long distances: one banded immature bird moved from its natal territory at Cowell, South Australia to Fraser Island, Queensland, a distance of approximately 3000 km (Marchant & Higgins 1993). Some birds (including some adults) may travel inland along major rivers (del Hoyo et al. 1994; Marchant & Higgins 1993). Birds also occasionally visit inland lakes, rivers or reservoirs that occur outside of the usual distribution of the species (Marchant & Higgins 1993). The White-bellied Sea-Eagle breeds in pairs. Each pair defends a breeding territory (primarily against other sea-eagles, particularly immature birds, and Wedge-tailed Eagles), which consists of a small area around the nest (Hollands 2003; Marchant & Higgins 1993). Though breeding territories may be occupied throughout the year (Hollands 2003), at least some adults will leave their nest sites (usually when young depart the nest) for a time and, consequently, leave their territories unguarded (Favaloro 1944; Marchant & Higgins 1993; Tarr 1962). Home ranges occupied by the White-bellied Sea-Eagle can be up to 100 km² (Mooney & Brothers 1986). Within these home ranges, breeding territories are typically located close to bodies of water (Emison & Bilney 1982; Marchant & Higgins 1993). Threats The main threats to the White-bellied Sea-Eagle are the loss of habitat due to land development, and the disturbance of nesting pairs by human activity (Bilney & Emison 1983; Clunie 1994; Dennis & Lashmar 1996; Mooney & Brothers 1986). The clearance of habitat (especially nesting habitat) and the subsequent influx of human populations have been implicated in past declines in sea-eagle populations in NSW, Victoria and South Australia (Bell 1983; Bilney & Emison 1983; Clunie 1994; Dennis & Lashmar 1996; P. Olsen 2005a, pers. comm.; Quinn 1969). Land clearance reduces the amount of suitable habitat available to the sea-eagle, and this can force birds to nest in sub-optimal habitats where their breeding success is greatly reduced (Emison & Bilney 1982; Bilney & Emison 1983). The intensity and spread of coastal development is, presumably, likely to increase in future, as is the resultant pressure on White-bellied Sea-Eagle habitat and, subsequently, the sea-eagle itself. The White-bellied Sea-Eagle is sensitive to disturbance when nesting, especially during the early stages of the breeding season, and may desert nests and young if confronted by humans or exposed to human activity (Clunie 1994; Hollands 2003; Mooney & Brothers 1986; Stokes 1996). The disturbance of nesting pairs by human activity can thus lower breeding success, and has been associated with some local population declines, for example, abandoned territories on the Eyre Peninsula and far west coast of South Australia were located in areas that had been developed for tourism or that contained recreational sites accessible by vehicles (Clunie 1994; Dennis & Lashmar 1996; Mooney & Brothers 1986). Abandonment of nesting sites on Kangaroo Island also followed developments in the areas (Dennis & Baxter 2006). The frequency and intensity of disturbance is likely to increase in future as human populations continue to expand and increase in density. Potential threats to the White-bellied Sea-Eagle include poisoning, shooting, competition with Wedge-tailed Eagles, and the deterioration of inland water resources. Poisoning could occur through the ingestion of baits intended for other animals (dogs, foxes), or through the ingestion of poisoned prey items (rabbits) (Barnett 1980; Bilney & Emison 1983; Clunie 1994; Favaloro 1944). The poisons most likely to be encountered by sea-eagles are pesticides (1080, DDT) and heavy metals (mercury, lead). For example, 1080 has been attributed to the deaths of some sea-eagles in Australia (despite the fact that raptors are generally thought to have a low susceptibility to 1080) (Clunie 1994), organochlorine pesticides (DDT) have been recorded in low to moderate (and apparently benign) levels in sea-eagles and their prey in South Australia (Falkenberg et al. 1994), and mercury has been found in high concentrations in some prey items (mullet, European Carp) in south-eastern Victoria (Clunie 1994; Glover et al. 1980; Smith 1976). The ingestion of poisons can lead to direct mortality (Barnett 1980; Clunie 1994; Mooney & Hunt 1983) or, as demonstrated in populations of closely-related raptor species overseas, reduce breeding success (Newton 1979). The historical and current impacts of poisoning upon Australian populations of the White-bellied Sea-Eagle are unknown (Clunie 1994), although a study has shown that the thickness of sea-eagle eggs has decreased since the introduction of DDT into agricultural practices Australia in 1946 (Olsen et al. 1993). The impact of pesticides is likely to be of less significance in future, given that the use of DDT has been banned in Australia since 1987 (although metabolites continue to persist in the environment, and will do so for several years) (Clunie 1994; Falkenberg et al. 1994), and that contemporary 1080 baiting programs aim to minimise the risk of secondary poisoning (Clunie 1994). However, the likely future impacts of heavy metal contamination are unknown. Shooting is known to be a cause of mortality (Clunie 1994; Favaloro 1944; Lamm 1965; Mooney & Hunt 1983), and is claimed to have been the cause of declines in some local populations in South Australia (Dennis & Lashmar 1996). Like the Wedge-tailed Eagle, the White-bellied Sea-Eagle sometimes feeds on domestic livestock (sheep, goats, chickens) (Marchant & Higgins 1993), which could make it a target for persecution (shooting, poisoning) by farmers (Mooney & Hunt 1983). The historic, current and future impacts of shooting upon the White-bellied Sea-Eagle are unknown. However, the current and future impacts of shooting on the population as a whole are likely to be minor given that the White-bellied Sea-Eagle is, as a native species, protected by national and state legislation. The White-bellied Sea-Eagle has a similar diet, and nests in similar sites, to the Wedge-tailed Eagle. Competition for resources between the two species could be having an adverse affect on some sea-eagle populations (Clunie 1994; Spencer & Lynch 2005). An increase in competition for nesting habitat between the White-bellied Sea-Eagle and Wedge-tailed Eagle has been recorded in Tasmania in recent years, and this has caused breeding failures in both species (Spencer & Lynch 2005). The impact of resource competition upon the long-term survival of the White-bellied Sea-Eagle is not known. However, it is possible that the incidence and intensity of competition may increase in future if the nesting habitat used by these species is subject to further clearance and development. The presence and persistence of the White-bellied Sea-Eagle in inland locations depends on access to substantial bodies of water, e.g. the inland distribution of the species is limited to sites that occur in the vicinity of major waterways or waterbodies. Processes that affect the quality or availability of inland water systems (such as increased sediment input into rivers and streams due to erosion, drainage of wetlands for agriculture, flood mitigation works) could, potentially, have adverse effects on inland populations of the sea-eagle (Clunie 1994). However, the actual historical and current impacts, and likely future impacts of these processes, are unknown. Inbreeding (and its consequent effects on genetic variability) had been identified as a potential threat to the White-bellied Sea-Eagle in Victoria, on the basis of the population size numbering 100 pairs or less (Clunie 1994). However, recent DNA studies have shown that neither the Victorian population nor other small populations (such as Tasmania) are genetically isolated, and that a high degree of gene flow exists between sea-eagle populations in different regions of Australia (Shephard 2004; Shephard et al. 2005b). Collision with wind turbines have also been identified as a potential threat to the White-bellied Sea-Eagle. Raptors are thought to be at higher risk of collision due to their tendancy to make flights in the swept area (Renewable Energy Pty Ltd Hobart 2007a). However, a number of studies have found that the risk of collision is extremely low, with birds avoiding the swept area of the turbine blades in over 99% of cases (Biosis Research 2007; Renewable Energy Pty Ltd Hobart 2007b; Smales 2005a). There are also occasional records of birds drowning after becoming entangled in fishing nets (Clunie 1994; Favaloro 1944). The White-bellied Sea-Eagle is not known to be especially susceptible to any catastrophic threats. Severe drought could possibly lead to declines in some inland populations, but the mobility of the birds should allow them to abandon these sites and then return again once conditions improve (Olsen 2005a pers. comm.). The White-bellied Sea-Eagle is a long-lived species that is capable of surviving for up to 30 years in the wild (PWS Tas 2006). Because of this longevity, it is possible that past or current declines in reproductive success may only become apparent when the current generation of mature birds has expired (Clunie 1994). Category:Birds Category:Birds of Prey Category:Carnivores Category:Predators Category:Raptors Category:Eagles Category:Asian Animals Category:Australian Animals Category:Endangered Species